Make multiple smaller weapon animation clips out of big default action for use in Unity game engine
The easiest in my opinion way to do that is to bake the animation fragments to new actions, separate for each desired state. To do that, use Action>Bake Action which you find in left tab (appears and disappears after pressing "T"). You'll achieve desired bake length by restricting animation time on the timeline to each state duration. After baking just move keyframes of created this way new action to the timeline beginning and voila.
You can get rid of unnecessary action by removing it from the mesh (or whatever else it's assigned to) in Action Editor (click on X icon on the right from the action name) and then choose Orphan Data in Outliner Search menu and click on Purge All. (this way you will get rid of all actions, textures, materials etc. that have no user permanently, so be careful to check everything first).